The present disclosure relates to a non-aqueous electrolyte secondary battery having a spirally-wound battery element.
In recent years, cordless or portable electronic devices, such as cellular phones and laptop personal computers, have advanced, and a thin, small, and lightweight portable electronic devices have been developed. The electronic devices have increased functions and hence need increased electric power. For this, there is an increasing demand for battery as an energy source of the electronic devices to satisfy the requirements of high capacity and lightness in weight.
As a secondary battery that meets the demands, for example, with respect to the non-aqueous electrolyte secondary battery utilizing doping with lithium ions and dedoping, various proposals have been made.
The non-aqueous electrolyte secondary battery has a positive electrode including a cathode active material layer using a lithium composite oxide, such as LiCoO2 or LiNiO2, formed on a positive electrode current collector, and a negative electrode including an anode active material layer using a carbon material capable of being doped with lithium and dedoped, such as graphite or a hardly graphitizable carbon material, formed on a negative electrode current collector. A separator is disposed between the positive electrode and the negative electrode, and they are spirally wound together to form a battery element. The non-aqueous electrolyte secondary battery having such a structure has an increased area for the reaction of electrodes, thereby achieving excellent discharge characteristics.
For improving the safety, the above non-aqueous electrolyte secondary battery has a structure such that, as described in Japanese Unexamined Patent Application Publication No. 2000-188115, Japanese Unexamined Patent Application Publication No. 2001-266946, and Japanese Unexamined Patent Application Publication No. 2005-347161, at the respective winding terminal ends of the positive electrode and negative electrode, portions onto which the active materials are not applied. That is, a positive electrode current collector exposed portion and a negative electrode current collector exposed portion are formed so that the voltage can be quickly lowered, for example, even if the battery is penetrated with a metallic nail or the battery is crushed by an external pressure, thus minimizing the damage of the battery. In this structure, an insulating material is formed on a portion which is likely to damage the separator or which easily causes short-circuiting, preventing the occurrence of short-circuiting and the like. The examples of the portions on which the insulating material is formed include: the positive electrode end and negative electrode end having burrs or the like caused due to the cutting of electrode, portions opposite to these electrode ends, portions having steps such as an end of the cathode active material layer and an end of the anode active material layer, and portions opposite to these ends.
In the above patent documents, a resin material having a high melting point, such as polyimide (PI), polyphenylene sulfide (PPS), or polyethylene terephthalate (PET), is used as an insulating material. The use of the high melting-point resin material enables to maintain the insulation effect without melting the covering material even when the temperature inside the battery is elevated.
However, when a battery charger malfunctions or a battery pack having incorporated the non-aqueous electrolyte secondary battery is mistakenly used, there is a possibility that the temperature in the non-aqueous electrolyte secondary battery is elevated and heat remains inside the battery, so that short-circuiting occurs through the positive electrode current collector and negative electrode current collector. In such a case, the battery having the structure described in Japanese Unexamined Patent Application Publication No. 2000-188115, Japanese Unexamined Patent Application Publication No. 2001-266946, and Japanese Unexamined Patent Application Publication No. 2005-347161 cannot achieve discharge of the battery quickly, and causes large temperature elevation in the battery, whereby the non-aqueous electrolyte secondary battery or battery pack becomes deformed.
Accordingly, it is desirable to provide a spirally-wound non-aqueous electrolyte secondary battery having improved safety.